In the book, The Fourteenth Goldfish, by Jennifer L. Holm, it follows a girl named Ellie. She is young and her parents are divorced. She has a very weird grandpa and he finds out the key to rebirth and the fountain of youth. He got kicked out of his lab and the jellyfish that made the fountain of youth is still there. They have to go and get it before it is too late.
The problem in the story is that her grandfather is now a teenager again and he left the secrets in the jellyfish at the lab. They had many road blockers that they had to try and try again to get into the lab. With their love of science, they had to get it before it went away.
I think grades 3-6 would like this book because it is a very funny book and it is not that complicated to read. I would rate it a 4 out of 5 because I wish that there was a little more action involved with the plot. I like this book because of the funniness that the grandpa says/ does. https://www.goodreads.com/review/show/2583320670